Examination of the flagellar organelle and the structure components necessary for flagellar function has revealed a complex system including at least thirty genes. The polypeptide products of these genes are localized in the cytoplasm, the inner cell membrane and the outer membrane. The function of the organelle depends, both on the structural components of the flagella and on other proteins that are integral membrane components or that are transiently associated with the membrane and are found in the cytoplasm. Genetic experiments allow identification and localization of these components. Furthermore, they can be arranged into groups involved in flagellar specific functions. Thus, for example, two gene products motA (39,000 daltons) and motB (31,000) are integral membrane components that are necessary for flagellar rotation. The flaK, flaL, flaV, flaM, flaS and flaT genes code for structural components of the hook-basal portion (the rotor) of the organelle. The che genes cheA, cheW, cheY are cytoplasmic components and the cheX, cheB, and cheZ genes are found in both the inner membrane and the cytoplasm. They all function to transmit signals from the terminal receptor of the chemoreceptor system to the flagellar rotor. The cheD (tar) and the cheM (tas) genes code for products that are integral membrane proteins and serve as the terminus of the chemoreceptor pathway and the beginning of the general chemotaxis pathway. They integrate signals from chemoreceptors and they are acted upon by the other che gene products. We have, therefore, a general view of the flagellar gene functions. Further experiments will be designed to establish the specific roles that these gene products play and to understand the molecular relationships between them, both in terms of their interaction and in terms of the flow of information and energy necessary for flagellar function. The work supported by this grant will be specifically directed toward finding out if the mechanisms involved in the flagellar system are general mechanisms and what role they play in disease and interaction with host cells.